Field of the Invention
This document relates to a liquid crystal display and, more particularly, to a liquid crystal display and its fabrication method capable of increasing a contrast ratio while reducing a scattered reflection from a surface.
Discussion of the Related Art
A liquid crystal display (LCD) displays images by adjusting light transmittance of liquid crystal by using fields. The LCD is divided into a vertical field application type LCD and a horizontal field application type LCD according to the direction of fields that drive liquid crystal.
The vertical field application type LCD drives liquid crystal in a twisted nematic (TN) mode by vertical fields formed between pixel electrodes and common electrodes disposed in a facing manner on upper and lower substrates. The vertical field application type LCD is advantageous in that it has a high aperture ratio but disadvantageous in that its viewing angle is narrow.
The horizontal field application type LCD drives liquid crystal in an in-plane switching (IPS) mode by horizontal fields formed between pixel electrodes and common electrodes disposed to be parallel on a lower substrate. The horizontal field application type LCD has an advantage that its viewing angle is relatively very large.
The horizontal field application type LCD includes a thin film transistor (TFT) array substrate (i.e., lower plate) and a color filter array substrate (upper plate) attached in a facing manner, spacers uniformly maintaining a cell gap between the two substrates, and liquid crystal filled in the cell gap.
The TFT array substrate includes a plurality of signal wirings and TFTs for forming horizontal fields by the pixel, and an alignment film coated thereon to align liquid crystal. The color filter array substrate includes color filters for color implementation, black matrixes for preventing light leakage, and an alignment film coated thereon to align liquid crystal. Liquid crystal varies light transmittance by the horizontal field formed between the pixel electrodes and common electrodes.
In the LCD, generally, the pixel electrodes and the common electrodes are formed as a single transparent conductive film or a single metal film.
When the pixel electrodes and common electrodes are formed as a single metal layer, respectively, metal with high reflexibility has strong qualities of reflecting external light made incident to a display surface. The reflected external light causes constructive interference or destructive interference with light made incident from a backlight of the LCD, which then passes through a polarizer, causing a spot with a diffraction pattern generated on a display image of the portion where external light has been reflected.
If the pixel electrodes and the common electrodes are formed as a transparent conductive film to reduce reflexibility, although the reflexibility is lowered, quality of black luminance is degraded due to an increase in transmissivity, resulting in degradation of a contrast ratio.